In relation to a needleless syringe with which the injection is performed without using any injection needle, a construction is adopted in some cases such that an injection component is injected or discharged by applying a pressure to an accommodating chamber in which an injection solution is accommodated, by means of a pressurized gas or a spring. For example, in the case of a needleless syringe disclosed in Patent Document 1, an injection solution, which is enclosed by an upstream side piston plug and a downstream side piston plug, is pressurized and allowed to flow into the nozzle, and thus the injection solution is discharged from the discharge port (injection port) thereof. In this situation, the pressurized injection solution is allowed to flow all at once into the nozzle which is in the atmospheric pressure state. Therefore, the pressure, which is received by the main nozzle body from the injection solution, is extremely changed. For this reason, for example, it is feared that the nozzle may be deformed and/or destroyed, and any noise may be generated during the injection.
On the other hand, for example, in the Patent Document 2, such an arrangement is disclosed that the interior of the nozzle is made filled with a part of an injection solution before injecting the injection solution by using a needleless syringe. Specifically, as shown in FIG. 2 of Patent Document 2, such a state is given before the use of a syringe that the accommodated injection solution is prohibited from flowing to the side of the nozzle by means of a ball valve which functions as a sealing member for an accommodating chamber for the injection solution. When the syringe is used, a grip of a main syringe body is twisted or screwed, and thus the ball valve is relatively moved in the main syringe body. A communicated state is given between the accommodating chamber and the nozzle by means of a groove arranged in the vicinity of the ball valve (see FIG. 4 of Patent Document 2), and the nozzle is made filled with the injection solution.